1. Technical Field
The present invention relates generally both to devices for conveying or storing gasses and to structural elements such as columns, beams, struts, and the like. More particularly, the present invention relates to a light weight inflatable pneumatic structural members deployed into serviceable condition by internal gas pressure. Even more particularly, the present inventions relates to a multilayered pressure vessel suitable for use in storing and conveying gasses, and especially well-suited for use as an inflatable load-bearing element. Also disclosed is a method of manufacturing the same.
2. Background Art
By definition pressure vessels comprise those vessels that have an internal pressure higher than the external atmospheric pressure. Such vessels include those that contain fluids, i.e., fluid storage tanks, and those that convey fluids, such as hoses. It is known to fabricate pressure vessels of flexible rather than rigid material, as this offers a reduction of mass and storage volume compared to rigid material systems. However, it is a relatively recent development in the technology of structural materials to compose columns, beams, struts, trusses, and the like, of inflatable rather than rigid materials. This advancement is still becoming fully appreciated, and the contemplated fields of use continue to expand rapidly.
In manufacturing inflatable structural members, the primary structural requirements that inform the design and selection of materials include: (1) general compressive buckling; (2) beam stiffness and natural frequency; and (3) beam bending buckling. Design parameters include: (1) the radius of the tube; (2) tube thickness; (3) tube length; (4) the modulus of elasticity; and (5) material density. Inflatable structural members have been devised to possess sufficiently desirable structural characteristics to enable use in a variety of fields. Inflatable structural members are even contemplated for use in extreme and exotic environments, most notably outer space.
For instance, as noted by S. L. Veldman and C. A. J. R. Vermeeren in Inflatable Structures in Aerospace Engineering—an Overview (April 2001), inflatable circular cylindrical beams are able to support structures such as solar array systems, telescope mirrors, sun shields and solar sails, truss structures, and the like. They may also be employed in permanent and temporary inflatable space habitats, and even in reentry and recovery vehicles. The authors note that in such applications, the low mass, low storage volume and ease of deployment are factors that reduce cost considerably.
More conventional applications are well known, and range across a diverse spectrum of possibilities, including columns, beams, booms, trusses, struts, cantilevers, shelters, linear actuators, ladders, antennas, masts, frame links, and so forth. The obvious advantage is that the potential structure may be transported to the construction site in a relatively collapsed or flat condition, perhaps on a reel or in racks, and it may then be deployed and installed in a structure. If rigidized, it may remain relatively permanent; if not, it may be collapsed for storage and transport once again.
The advantages of flexible structural members were recognized at least as early as 1968, when U.S. Pat. No. 3,364,623 was issued to the Canadian Peter Isaac. His patent discloses an inflatable structural member made of stiff resilient material which is normally flexible and capable of being stored on a reel, but becomes erectly rigid when inflated. The member is stored on a reeled state in the flexible state and may be fed from the reel in a rigid state in a cantilever manner without guidance other than from the reel. The member is capable of carrying tensile, compressive, or flexural loads after unreeled.
A later, though not significantly more mature, expression of the art is illustrated in U.S. Pat. No. 4,514,447, issued to Boxmeyer in 1985, which teaches a lightweight, inflatable structural member, having a substantially tubular shape and sealed at both ends, including an inner lining to maintain internal pressure upon inflation. The inner lining is covered with a filament reinforced matrix structure comprising resin impregnated filaments of high tensile strength. The uninflated structural member is stowable in a collapsed condition. Curing of the resin matrix is inhibited by storing the collapsed member at a low temperature. Prior to use, the member is inflated with a fluid and heated to enable curing of the resin matrix.
This method of manufacturing a rigid structural member by inflatable flexible material and coating or otherwise rigidizing the material with resin was recognized much earlier, in U.S. Pat. No. 3,138,506, to Ross, which discloses a method of manufacturing an article of stiffened fibrous material comprising the steps of providing a pliable article having spaced fibrous walls and ties connecting the spaced walls; inflating the fibrous article; applying a resin bonded fibrous material over the inflated article; and hardening the resinous band while the article is inflated to tension the material.
The foregoing patents reflect the current state of the art of which the present inventor is aware. Reference to, and discussion of, these patents is intended to aid in discharging Applicant's acknowledged duty of candor in disclosing information that may be relevant to the examination of claims to the present invention in various national offices. However, it is respectfully submitted that none of the above-indicated patents disclose, teach, suggest, show, or otherwise render obvious, either singly or when considered in combination, the invention described and claimed herein.
Additionally, and as will be readily appreciated, the structural elements taught in each of Boxmeyer and Ross require more than pneumatic pressure to provide the desired structural characteristics, and after rigidization they are incapable of collapse for storage and transportability. Furthermore, the structural member of Isaac may be fabricated from flexible material, but the manufacturing process entails use of a tube to which upper and lower members, joined by hinges, are affixed. Thus, provision of an article already comprising a pressure vessel, namely a tube, is a predicate to the construction of the device shown in Isaac.
Accordingly, it would be desirable to provide a pressure vessel fabricated from flexible material that may be adapted for a variety of uses ranging from use as structural member when inflated, to use as a fluid conveyance means when uninflated and configured as a hose or filter. It would further be desirable that such a member be capable of collapse for easy storage and transport. Finally, it would be desirable to have an inexpensive and mechanically simple means of constructing such a pressure vessel.